The development of a non-volatile storage device provided with a memory cell array where memory cells are arranged three dimensionally is progressing. For example, a structure which includes a silicon substrate, a plurality of word lines which are stacked on the silicon substrate, and memory cell strings which penetrate these word lines is known. In the manufacturing of a non-volatile storage device having such structure, a memory film is formed on an inner wall of a memory hole which penetrates the plurality of word lines, and a semiconductor film is formed on the memory film in the memory hole. With such a configuration, a plurality of memory cell strings which extend in the direction perpendicular to the silicon substrate can be formed. However, as miniaturization of the memory cells progresses, the size of memory hole becomes finer which creates a possibility that the memory hole may be closed during the step of forming the memory film. When the memory hole is closed, the semiconductor film cannot be formed within the memory hole and hence, the memory cell string will not function.